Laminated element provided with a heated layer

ABSTRACT

A laminated panel element that includes at least two rigid panes, for example glass panes, bonded to each other on their surfaces, which are each provided, over their whole surface, with an electrically conductive coating that can be heated by application of a voltage via electrodes. One of the two rigid panes is provided with a cut-out allowing the passage of external electrical connections that are in electrical contact with the two coatings.

The invention relates to a laminated panel element with a heating layerthat has the features presented in the preamble of claim 1.

Such heater elements applied to glass or other nonconducting substratescan be used as radiative heater units if the installed heating power isadequate for this purpose. These heater elements can be installed on orin building walls or be integrated into these buildings as a replacementfor the usual (central) heating units. For this purpose, they do notneed to be implemented in the form of windows but can equally well be inthe form of mirrors, decorative surfaces, etc. Alternatively, it is alsopossible for such panel elements to be used as a general means toproduce heating from the surfaces of technical appliances, for exampledomestic appliances, where their limited installation height and smooth,easily-cleaned surfaces offer big advantages.

The power requirements of large-area heating layers demand the use ofrelatively high voltages. Safe and reliable electrical isolation musttherefore be provided, particularly along the edges of the panelconcerned, which may be coated over its whole surface.

The document DE-A1 198 60 870 describes a panel heater element of thistype, with a glass substrate and its whole surface coated. In order toensure safe and reliable isolation from the outside of the electricallypowered coating, a region forming a frame around the periphery of thecoating is isolated by a separation line and is thus electricallyneutralized. Such an arrangement also protects the coating fromcorrosion that penetrates in from the outer edges, but that can onlypenetrate as far as the separation line.

The electrical connections to the heating layer are connected to thecoating situated on the inside of the surface surrounded by this frame,other separation lines defining a heating current path over the wholesurface of the coating. The same document also discloses the option thatconsists in coating with an electrical conductor two or more of thebonded panes of a laminated or safety glazing panel. The details of thepractical implementation of such a laminated pane will not however beentered into here, either as regards the electrical connections or theelectrical control of such a double heating layer.

In another known panel element (document DE-B-2 113 876), theelectrically conductive heating coating does not extend right up to theedge of the panel, such that a spacer frame for an insulating glazingpanel can be bonded, without any special arrangements, directly onto theborder (where there is no layer) of the glazing panel. The electrodepower supply conductors pass through sealed feed holes formed in thespacer frame. The second pane of the insulating glazing panel has anon-heating solar protection layer.

The prior patent application 102 41 728.8 of the Applicant describes aconnecting device for a laminated panel element that comprises a firstrigid pane having a heating layer together with a second rigid panejoined over its whole surface with the first by adhesion. The connectingdevice is inserted into a feed hole formed in one of the rigid panes. Itcomprises contacts that allow a direct contact with the heating layer tobe established. For this purpose, the latter has at least two electrodesthat are disposed in the region of said cut-out. A plurality of currentpaths, electrically connected in parallel and formed within the coating,can run between these electrodes.

The length and width of the current path or paths together with thesurface conductivity (expressed in ohms per square) of the layerconfiguration used will determine the consumption of electrical energyand the heating power of the panel element. Depending on the particularpower supply voltage available or predetermined, various heating powerscan be established over wide ranges by the current path pattern, themaximum admissible temperature also depending on the type of use of thefinished panel element. If, for example, it is not possible for the userto come into direct contact with it, or this need not be assumed, thetemperatures can be well above 50° C. However, care must of course betaken to ensure that coatings adhering to the coated pane, for exampleadhesive layers of a laminated glazing panel, are not degraded at thetemperatures that may be reached during normal operation.

In the literature, various materials are mentioned that are suitable forsuch heating layers. Solely as examples, indium tin oxide (ITO) andmetals that are good conductors such as gold, silver, copper or aluminumare mentioned here. Layer configurations having dielectricantireflection layers and at least one metallic layer situated betweenthem allow very good transmission of visible light with satisfactoryelectrical conductivity, but can also be used, at the same time, asinfrared reflectors. Such typical layer configurations exhibit sheetresistances in the range of 1 to 4Ω per square.

When these heater elements operate at high heating powers, the adhesivelayer, generally a thermoplastic (preferably, a PVB, PMMA or EVA sheet),can reach its thermal limits. The adhesion to the (coated) glasssurfaces may fail when the full heating power is applied for asufficiently long period. In some cases, and in particular at highcurrent density locations, this can lead to local delaminations of thecoating. Since, for reasons of production method and cost, moving awayfrom the adhesives tried and tested over several years in laminatedglass manufacturing is undesirable, other means of avoiding thesethermal problems must be found.

The object of the invention consists in solving this problem byproposing a better laminated panel element with heating layers.

According to the invention, this problem is solved with the features ofclaim 1. The features of the dependant claims present advantageousdevelopments from this subject.

Firstly, with a double coating, the option is proposed which consists inobtaining the same heating power as with a single coating without asignificant increase in the heater unit volume, the layer thicknessesbeing in the nanometer range with a much lower current per unit area foreach coating. Heat is not then produced in only one of the interfacelayers situated between a glass panel and the adhesive layer.Furthermore, the thermal loading of the connection electrodes, throughwhich all the current must flow into all the current paths, is reduced.Another feature of this configuration according to the invention residesin the fact that the two coatings are electrically connected via a flatside of the panel element, owing to the fact that one of the two panelshas a cut-out that allows the passage of external connections.

In a first advantageous embodiment of the invention, the two coatingsare disposed on either side of the adhesive layer that joins the tworigid panes. In a second advantageous embodiment which, depending on thethickness of the rigid panes, may yield a slightly greater totalthickness for the laminated panel element, a third rigid pane isprovided and at least one heating layer is disposed on each side of thethird rigid pane. In particular, it is not absolutely necessary that thecentral pane hold the two heating layers, several variant arrangementsbeing possible, as will be explained in more detail below.

Other combinations of the two variants may also be implemented where aneven greater distribution of the heating power is desired, and, ifrequired and within the scope of the present invention, other rigidpanes (coated or uncoated) may also be added.

In all the configurations, the distribution of the heating can becontrolled, on the one hand if the two coatings are identical and arepowered by identical supply voltages (preferably, the normal mainsvoltage in the country concerned (for example, 110 or 230 VAC)).

In an advantageous development, the coatings that each form one or moreresistive heater elements (in parallel) can each be used separately fromone another or be used in a series or in a parallel circuit.

In the latter case, the highest heating power can be obtained; thelatter can be used, for example, for heating the heater element whenstill cold, returning to a lower heating power for the longer-termoperation.

The configuration according to the invention however also allows the twocoatings to be provided with completely different properties. On the onehand, they may be made of different materials. Their resistances can beadjusted over wide ranges, for example by the choice of the specificconductivity and/or of the internal structure of the layerconfiguration, such that different heating powers are obtained even forthe same applied supply voltage.

On the other hand, the coatings may also be applied with variousthicknesses. Thus, the sheet resistances can again be adjusted dependingon whether the coatings of various thicknesses are formed from identicalmaterials or from different materials.

In addition, especially in the case of transparent panel heaterelements, the choice of material also allows a desired coloredappearance to be obtained. For example, a gold coating has a more orless pronounced red or golden tint, whereas layers of silver have a moreneutral tint.

It is clear that, in a manner known per se, on a panel element accordingto the invention, two or more current paths may also be provided which,if required, may be connected independently of one another, withineither or both of the coatings, in order to be able to connect anddisconnect the heating power in stages if needed. This will depend onthe number of contacts or electrodes available on the coatings.

During the manufacture of panel heater elements not to be used aswindows, the antireflection coating of the conducting layer itself, forexample made of silver or another conducting metal, could be eliminatedwhich, on the one hand, would simplify the power connections (dielectricantireflection layers are usually nonconducting or are poor conductors),and on the other hand, would allow decorative effects to be obtained onthe surface. The precise determination of suitable materials for theconfiguration of heating layers is however left to the discretion ofthose skilled in the art who have the task of calibrating the desiredheating power.

As an extra feature, one or more temperature probes can be provided fordetecting the effective temperature of the panel element. Suchtemperature probes may even be implemented in the form of currentlimiters (for example, cold conductors whose electrical/ohmic resistanceincreases with temperature). As a variant, a separate switchingmechanism can be provided for disconnecting the heating power if thereis a risk of overheating of the panel element, where this mechanism canbe controlled by a temperature probe.

In a particularly advantageous manner, the panel element according tothe invention can be equipped with a connecting device of the typedescribed in the aforementioned prior application. It is possible toconnect the two heating layers simultaneously to a single connectingdevice which will be disposed in the cut-out of one of the panes. Theelectrical connections of the heater element can thus be advantageouslygrouped in a very compact fashion. At the same time, the connectingelement can comprise the switching elements necessary for controllingthe heating power of the heater element. These are, in particular,elements for the independent control of one or both coatings, and, whererequired, of two or more independent current paths situated within oneor both coatings, which elements allow parallel or serial connections tobe established, together with, in some cases, switching elementscontrolled by thermoprobe. Lastly, as a safety cut-off, switchingelements can be provided that are required in case of possible ruptureof the glass heater element.

This connecting device has the advantage of being able to be mountedafter the manufacture of the laminated panel element and also of beingable to be removed from it, if needed. It is particularly preferablethat the connecting device be fitted with removable contact means, forexample plug or spring contacts. For relatively high supply voltages ofthe laminated panel element, they only have to transmit small (AC)currents; in addition, heater elements used in buildings are not, as ageneral rule, subject to vibrations. Thus, problems of corrosion shouldnot be expected which, in other fields of application (vehiclemanufacture), can have the effect of reducing the contact efficiency byincreasing the contact resistance. Furthermore, the connection orcontact area may, if necessary, be hermetically sealed in order toprevent dampness or dirt penetrating into the system.

If necessary, the electrical contacts onto the active elements or, asthe case may be, onto their electrodes can, however, also be attached bysoldering or only be protected as an option. Soldering techniques areknown that allow the soldering points to be melted reliably withoutdirect contact with the heat source (induction or laser soldering) orwhich can even be used through the coated pane without however damagingthe coating.

A panel element equipped according to the invention may be used as astand-alone heating unit. It can also be integrated into an insulatingglazing panel in which it is joined to another pane via a separationframe. It is clear that other (glass) panels may also be included withina laminate joined over its whole surface to the two rigid panes of thepanel heater element without, by doing this, straying from the idea onwhich the invention is based.

Other details and advantages of the subject of the invention will becomeapparent from the figures of an exemplary embodiment and a variantembodiment and from the description which is presented in the followingsection.

In simplified drawings that are not to scale,

FIG. 1 shows a cross-sectional view of a laminated panel elementaccording to the invention in the region of a connecting device, twoelectrical heating coatings being disposed on either side of a singleadhesive layer, and

FIG. 2 shows a cross-sectional view of a variant of the laminated panelelement according to the invention having a third rigid pane and twoelectrical heating coatings situated on either side of the central rigidpanel.

In FIG. 1, a panel heater element 1 according to the invention isfabricated in the form of a laminated glazing panel having a first rigidpane 2, an adhesive layer 3 and a second rigid pane 4. The two rigidpanes 2 and 4 are preferably thermally prestressed, or partiallyprestressed. On their flat sides facing the adhesive layer 3, each ofthe two panes has a heating layer 5. Only a part of the thickness of therigid pane 2 is shown and a double transverse dashed line on the rigidpane 4 indicates that its thickness shown has also been truncated. Itwill be understood that these two rigid panes are considerably thickerthan the adhesive layer 3.

The heating layers 5 consist of compositions and/or successions oflayers that are sufficiently resistant to the thermal stresses when theyfunction as surface heating layers and that are suitable for theparticular application and, where required, for the pane prestressing.Suitable layer configurations have been described in numerous variantsin the prior art, so that these does not need to be considered furtherhere. Layer configurations with a high visible light transmission can beimplemented that are therefore transparent.

For example, a coating marketed by the Applicant under the name of“Planitherm 1.3” can be used, where the number represents it k index.This is a layer configuration with a high thermal resistance and capableof being prestressed, having a silver layer and dielectricantireflection layers on both sides of this layer, and which alsopossesses infrared reflection properties.

However, depending on the requirements, other electrically conductinglayer configurations may, of course, also be used. Their sheetresistance will need to be in the range from 1 to 25 ohms per square.The lower the sheet resistance, the larger can be the flat heaterelement that must be heated with a given voltage.

Suitable means ensure, in a manner known per se, the peripheralpassivation of the coatings 5 along the edges (not shown here) of thepanel element, in other words that there is no electrically conductingcontact with either its outside surface or with its front surface, noris there any risk of corrosive attack of the layer material from theoutside. In any case, a hermetic covering of the border gap is obtainedby means of the synthetic thermoplastic adhesive that forms the adhesivelayer 3 (for example, polyvinyl butyral (PVB), ethylene/vinyl acetate(VA)). It will be understood that the adhesive layer material must bechosen to be compatible with the material of the coating 5.

The cross-sectional view shows the essential components of theelectrical power supply of the two heating layers 5 in a commonconnection area. Each of them has (at least) two plane electrodes 6 thatare disposed on both sides of an insulating separation line 7 thatisolates two electrical poles of the heating layers 5 from one another.The heating layers 5, which are initially deposited continuously, aredivided, in a manner known per se, into current paths by structure linescreated later. This defines the current paths between the two pairs ofelectrodes 6, such that the current flows over the whole surface of thepanel element. The current paths (not shown here) can be, but are notrequired to be, identical for the two coatings 5.

The electrodes 6 of the two layers 5 can also, depending on therequirements, be implemented in the same or in different ways. The samecurrents will not necessarily be required to flow, nor will the sameheating power necessarily be expected, in both coatings 5 for allapplications.

The electrodes 6 themselves are opaque and cannot be visible from theoutside. Consequently, they can also be configured as decorativeelements, for example representing the logo of a firm or manufacturer.

Unlike the succession of layers shown, the electrodes 6 may also bedeposited under the coatings 5, in other words before their depositiononto the glass surfaces. They can take the form of thin metal foils orelse as ribbons of conductive screen-printing paste that can be baked(during the prestressing of the panes). Suitable embodiments ofelectrodes, which are also referred to as collection rails, have beenwidely described in the prior art. By coloring the conductivescreen-printing paste used for the electrodes, given colored effects canalso be obtained.

It is clear that, where necessary, the electrical contact area can bevisually masked by suitable means, for example by placing an opaquedecoration underneath it or by printing such a decoration onto it, orelse by using a very dark colored glass paste for the panes. As anexample, in the region of the electrodes the pane 4 has an opaquecoating 8 which is not electrically conducting and which was printedonto the surface of the glass before the deposition of the coating 5 andthen heat treated during the prestressing process.

In the connection area of the electrodes 6, a feed hole or a cut-out 9is formed in the pane 4 and in the adhesive layer 3. This allows thepassage of the external electrical connections for the two pairs ofelectrodes 6 of the two coatings 5. The cut-out in the adhesive layer 3is cut to size before the two rigid panes 2 and 4 are joined together,such that the adhesive material does not penetrate as far as theelectrodes 6 by melting. Where necessary, suitable protection measureswill be taken.

An insert 10 in the form of a bushing is fixed in the feed hole 9 of thepane 4. Its axial length corresponds substantially to the thickness ofthe rigid pane 4 (a few millimeters), and it penetrates as far as theplane of the adhesive layer 3. A radial shoulder 11 that overhangstoward the outside hooks onto the rear edge of the feed hole 9, suchthat the insert 10 is fixed there in geometric correspondence whichprevents it being extracted.

This insert must already be in place in the feed hole 9 before joiningthe two rigid panes 2 and 4. Only when the thermoplastic adhesive layer3 has melted will it be definitively fixed. It can be seen in thedrawing that the shoulder 11 is further held within the material of theadhesive layer 3.

The insert 10 forms the mechanical base of a connection housing 12. Twovertical dashed lines indicate a threaded link between the two partsallowing them to be separated. A support block 13 is fitted into thecenter hole of the insert 10 through the connection housing 12. Thisforms the base of two pairs 14, 15 of spring contacts that are pushedinto contact with the electrodes 6. The inside pair 14 of springcontacts is disposed at the lower end of a short axial appendage fromthe support block 13. The latter has a slightly smaller diameter orperiphery than the support block 13 itself. The spring contacts areplaced in direct electrical conduction on the electrodes 6 of thecoating 5 of the (lower) pane 2. The power supply or heating voltage isbrought to the coating of the rigid pane 2 by these contacts 14.

Although the spring contacts 14 suffice, in the intended application ofthe surface heater element 1 (relatively high supply voltage, ACcurrent), for the demands of a safe and durable electrical connection,if necessary, they can optionally be welded to the electrodes 6, inparticular with suitable pre-applied tinning, where the required heatcan preferably be supplied without contact (by induction or by laser).

The outside pair of spring contacts 15 extends from the support block 13at the shoulder formed at the transition with its appendage. The springcontacts 15 are not in direct contact with the surface electrodes 6 ofthe heating layer 5 of the (upper) rigid pane 4, since the latter mustterminate on either side of the feed hole 9. However, the insert 10 hastwo connecting bridges 16 for this purpose. On one side, they penetrateinto the center hole of the insert 10. They stop on either side of theappendage of the support block 13 and form the elements that aredirectly complementary to the spring contacts 15. On the other side,they pass through the wall of the insert 10 and rest on either sideagainst the (upper) surface of the shoulder 11 of the insert 10, namelythe surface facing the coating 5 of the pane 4.

After the insertion and the fixing of the insert 10 into the feed hole 9of the rigid pane 4 and after the bonding of the two rigid panes 2 and4, the shoulder 11 holds the connecting bridges 16 in contact with the(upper) flat electrodes 6. The insert 10 is screwed into the connectionhousing 12. In this way, the shoulder 11 is pulled with a prestressingagainst the flat electrodes 6 and this contact area is not particularlycritical. The surfaces of the connecting bridges 16 in contact with theflat electrodes 6 can be roughened or have points allowing a certainpenetration of the connecting bridges into the flat electrodes 6. Herealso, as has already been indicated above, by applying heat, additionalsoldering, with pretinning of the connecting bridges and/or of the flatelectrodes, can however be implemented.

The connecting bridges 16 are preferably fixed into the insert 10 sothat the connecting device can be assembled as easily as possible. Thiscan be achieved, for example, by coating the connecting bridges 16(narrow sheet-metal strips) with the synthetic material of the insert 10during its manufacture.

The support block 13 with the spring contacts 14, 15 is inserted intothe insert 10 in the correct position, if necessary by applying forcewith suitably fashioned elements, such that the spring contacts 14, 15come into contact with the corresponding complementary element(electrode, bridge contact), and is then fixed. The support block 13 canform an integral assembly with the connection housing 12 and be fixed atthe same time as the latter onto the insert 10. The axial and radialoffset between the pairs 14 and 15 of spring contacts allow directcontacts between them to be excluded.

The circuit symbols of a switch 17 and a transistor 18 represent theelectrical or electronic equipment of the support block 13 or of theconnection housing 12 and may each correspond to a plurality ofcorresponding elements. In addition to the passage of the electricalsupply voltage from the connecting cable to the electrodes 6, othercontrol and switching functions are attributed to this part of theconnecting device. In particular, these switching elements provide thevoltage-controlled power supply of one or of both of the coatingsdepending on the corresponding instructions from the external control aswas already explained above.

In the connection part, by means of the insert 10 and the support block13, one or more temperature probes (not shown) may also be maintained incontact with one or more coated panes 2 and 4 in order to detect theeffective temperature in the contact area of the electrodes 6.

A switching element can then evaluate the measured values from thetemperature probe and, if necessary, disconnect, at least momentarily,the current feed to one of the heating layers or both, if the effectivetemperature were to exceed an acceptable threshold. However, a switchingelement can also be provided that protects against temperature excessesand that, in a manner known per se, limits the electrical power consumedto acceptable levels.

At least one switching device, which may have an electronic orelectromechanical configuration, manages the current feed to the heatinglayers. This switching device may fundamentally be manually connectedlocally, be controlled by sensors, for example by the temperature probe,or by a window control device. As has already been indicated, the lattermay be part of an automatic temperature regulation system for thepremises (air conditioning installation, etc.), however it canfundamentally also be selectively controlled manually.

If the control signals are transmitted by wireless, a suitable receiverwill be provided in the connection housing 8 or in the support block 13,in addition to a decoder and other switching means (for example,amplifiers). If the control signals are transmitted by lines, suitableevaluation means will be provided for these, in particular where thecontrol signals are transmitted via already existing mains connectionlines and must be filtered at their input.

In a particularly advantageous embodiment, all of the electrical devicesor interfaces are thus assembled locally in the connection part of thepanel heater element 1.

After the connecting device has been built and its operation verified,if necessary, the transition between the pane surface and the connectionhousing 12 can be further made hermetically tight by a hermetic seal 19.Unlike the embodiment shown in the drawing, this hermetic seal may, ofcourse, be installed directly between the lower face of the connectionhousing 12 and the pane surface.

While the insert 10 can, in practice, be joined flush with the mainsurface of the rigid pane 4, the connection housing 12 will be slightlyprotruding from this surface. Since, in most cases, this side of theflat heater element 1 is not turned toward the observer or user in theinstalled position and/or is, for example, placed facing or within awall, the visibility of the connecting device on the mask (or,alternatively, on the opaque electrode 6 serving as a decorativeelement) remains limited, and moreover, the risks of unauthorized oraccidental handling of the connecting device are, in practice, excluded.Where an activation switch of a control unit for the connecting deviceneeds to be provided, this will, of course, be preferably installed inan easily accessible place, for example close to the edge of the flatheater element.

In FIG. 2, identical elements to those in FIG. 1 have been given thesame reference numbers. Here, the laminated panel element is equippedwith a third (lower) rigid pane 20 that is joined by surface adhesion tothe central rigid pane 2 by means of an adhesive layer 3. The surfacessituated at the top in the drawing of the two rigid panes 2 and 20 havea flat heating coatings 5. Once again, the two coatings 5 each have apair of electrodes 6. The explanation presented for FIG. 1 also appliesto the division of the coatings 5 and the current paths between the pairof electrodes 6, as well as to the electrical control and the operationin general.

Here also, the rigid pane 2 is crossed by a feed hole 21 that isoriented substantially axially with respect to the feed hole 9 of therigid pane 4. The second adhesive layer 3 has a corresponding cut-out inwhich the electrodes 6 of the lower coating terminate. An axialextension 22 of the support block 13 is inserted into the feed hole 21with the connection housing and the support block. Its diameter or, asthe case may be, its periphery is smaller than that of the support block13. There is a given amount of radial play between it and the wall ofthe feed hole 21, in order to compensate any possible differencesbetween the centers of the drilled holes 9 and 21 which could resultfrom the manufacture of the laminated pane. It extends in thelongitudinal direction up to just before the surface of the third pane20 situated in the laminate. Here also, contacts between the pairs 14and 15 of spring contacts are excluded by an axial offset and a radialoffset.

The spring contacts 14 shown in FIG. 1 are disposed here at the lowerend of the appendage 22 and rest on the electrodes 6 of the lowercoating 5 with an adequate contact pressure. On the other hand, thespring contacts 15 again extend from the shoulder of the support block13 formed at the transition with the appendage 22. They are situateddirectly on the electrodes 6 of the upper coating 5 of the central pane2.

In another variant (not shown) of the double-layer heater, it is, orcourse, possible to deposit a coating 5 on the lower surface of theupper pane 4 (as shown in FIG. 1) instead of depositing it on the uppersurface of the central pane 2, and to implement its contact in a mannercorresponding to that of FIG. 1.

While in the configuration shown in FIG. 1 a substantially identicalthermal radiation is emitted from both sides of the panel element (inthe case of a completely symmetrical implementation which therefore hasthe same electrical power for the two coatings and the same thicknessesfor the rigid panes), another arrangement of the coatings in thelaminate allows an asymmetric radiation to be obtained which, if thereis a need, could be wholly desirable.

In the same way, other combinations of layer arrangements, possibly withthree or more heating layers, still remain within the scope of theinvention described here.

1-17. (canceled)
 18. A laminated panel element comprising: at least tworigid panes bonded to each other on their surfaces, which are eachprovided, over their whole surface, with an electrically conductivecoating that can be heated by application of a voltage via electrodes,wherein one of the two rigid panes is provided with a cut-out, in aconnection area, allowing passage of external electrical connectionsthat are in electrical contact with the two coatings.
 19. The laminatedpanel element as claimed in claim 18, wherein two surfaces of the tworigid panes facing each other are provided with electrically conductivecoatings on either side of an adhesive layer that joins them.
 20. Thelaminated panel element as claimed in claim 18, further comprising atleast a third rigid pane joined on its surface, and wherein at least oneof the electrically conductive coatings is provided on both sides of thecentral rigid pane.
 21. The laminated panel element as claimed in claim18, wherein both or all of the coatings are electrically connected by aconnecting device disposed in a fixed manner in the cut-out.
 22. Thelaminated panel element as claimed in claim 18, wherein both or all ofthe coatings may be used individually selectively, within a seriescircuit and/or within a parallel circuit.
 23. The laminated panelelement as claimed in claim 18, wherein the coatings are composed of asame material and/or of a same layer configuration.
 24. The laminatedpanel element as claimed in claim 18, wherein the coatings are composedof different materials and/or layer configurations.
 25. The laminatedpanel element as claimed in claim 18, wherein current in at least one ofthe coatings always flows between two electrodes disposed within theconnection area along a predetermined path that is created by a locallyisolating division of the coating.
 26. The laminated panel element asclaimed in claim 18, further comprising a temperature probe fordetecting effective temperature of the heating coatings.
 27. Thelaminated panel element as claimed in claim 26, further comprising aswitching element configured to be controlled by the temperature probe,for interruption or reduction of heating current when a predeterminedtemperature threshold is exceeded.
 28. The laminated panel element asclaimed in claim 18, wherein at least the connection area is visuallycovered by a mask.
 29. The laminated panel element as claimed in claim28, wherein the visual mask is obtained by use of an opaque glass pastefor the prestressed pane.
 30. The laminated panel element as claimed inclaim 28, wherein the visual mask is formed by an opaque decoration. 31.The laminated panel element as claimed in claim 30, wherein the opaquedecoration is disposed as a thin layer between the surface of the paneand the heating coating.
 32. The laminated panel element as claimed inclaim 18, wherein the electrodes are formed by application and heattreatment of an electrically conductive screen-printing paste before orafter deposition of the heating coatings.
 33. The laminated panelelement as claimed in claim 32, wherein the electrodes are implementedin a form of visible decorative elements.
 34. The laminated panelelement as claimed in claim 18, wherein the coatings are electricallyconnected to the external connections by removable electrical contacts.35. The laminated panel element as claimed in claim 34, wherein theremovable electrical contacts include spring contacts.